1. Field of the Invention
The present invention relates to an antislip regulation and antilock braking system for vehicles equipped with a braking system comprising one or more brake cylinders each associated with one or more wheels, a source of fluid under pressure, and a brake control that is operated to effect braking by feeding said cylinders with fluid under pressure via one or more brake valves and one or more brake pipes.
2. Description of the Art
Braking systems including a brake master cylinder equipped with a reservoir are already known in the art and are used in particular in motor vehicles for use on roads. To effect braking, a volume of fluid that depends on the operating force applied to the brake pedal is transferred from the reservoir to the brake cylinder(s) via the master cylinder. When the brake pedal is released, the fluid returns to the reservoir. The reservoir is small and the above systems can be used only in applications in which transferring a very small volume of fluid is sufficient to operate a brake cylinder. Some motor vehicles are further provided with an antislip regulation and antilock braking system. In an antilock braking system, fast-acting solenoid valves reduce the fluid pressure in the brake cylinder as soon as a wheel associated with the cylinder tends to lock. In an antislip regulation system, if a wheel tends to slip, an auxiliary source of fluid under pressure assists braking of that wheel by feeding the associated brake cylinder.
For larger vehicles, and in particular for self-propelled agricultural and civil engineering plant, much greater volumes of fluid have to be transferred into the brake cylinders to effect braking. Consequently, the brake circuits generally comprise a pressure source which feeds fluid accumulators via a priority flow valve and a connector-disconnector. The fluid that feeds the brake cylinders comes from these accumulators, which are located far away from the cylinders.
WO 92/03321 proposes an antilock braking and antislip regulation system that uses a two-position control valve for each braked wheel that is adapted to connect the brake cylinder to a brake pipe connected to a brake fluid feed pipe or to a connecting pipe connected to a supplementary valve associated with the wheel.
If the wheel locks, the control valve connects the brake cylinder to the connecting pipe and the unoperated supplementary valve reduces the pressure in the brake cylinder. When the pressure has fallen sufficiently, the supplementary valve must be operated to connect the connecting pipe to an auxiliary pressure source to restore braking.
In the event of wheelspin, the control valve connects the brake cylinder to the connecting pipe connected to the supplementary valve, which is operated to connect the connecting pipe either to the auxiliary pressure source, to brake the wheel that is subject to wheelspin, or to the return line, to prevent excessive braking of the wheel.
The above system and its operation are relatively complex. Also, it is not the brake pipe that restores braking after a wheel has locked, which means that the level of braking cannot be controlled by the operator in the normal way.